Magnetic gear assemblies offer numerous advantages over counterpart mechanical gear assemblies. Magnetic gear assemblies provide a contactless mechanism for speed amplification (i.e. acoustic noises, vibrations, and wear and tear are all reduced), do not require lubrication (i.e. maintenance costs and pollution are both reduced), have inherent overload protection (i.e. slippage inherently replaces mechanical breakage), and have the potential for high conversion efficiency. Numerous conventional magnetic gear assemblies are known to those of ordinary skill in the art, typically including a plurality of permanent magnets arranged one directly next to another in adjacent or concentric rings or rotors around one or more axes, with steel poles or the like interspersed between the adjacent or concentric rings in an intermediate ring or rotor, for example. The result is selectively actuated relative rotation of the adjacent or concentric rings or rotors, as well as the intermediate ring or rotor, and speed amplification results. Typically, the flux fields of the magnets are purposefully magnetized in a radial direction.
For example, referring specifically to FIG. 1, one conventional magnetic gear assembly 5 includes an inner rotor 10 including P1 magnet pole pairs that rotates at angular velocity ω1, a middle rotor 12 including n2 ferromagnetic steel poles or the like that rotates at angular velocity ω2, and an outer rotor 14 including P3 magnet pole pairs that rotates at angular velocity ω3. The flux fields of the magnets are aligned as illustrated. If the relationship between the poles is chosen to be:P1=|P3−n2|,  (1)then the inner rotor 10 and the outer rotor 14 interact with the middle rotor 12, via flux linkage, to create space harmonics. The angular velocities of the rotors are related by:ω1=[P3/(P3−n2)]ω3+[n2/(n2−P3)]ω2.  (2)If the outer rotor 14 is stationary (i.e. ω3=0), then:ω1=[n2/(n2−P3)]ω2=Gω2,  (3)where G is the gear ratio. The above referenced flux linkage, and flux focusing, is illustrated specifically in FIG. 2.
Invariably, a rare earth material, such as a neodymium iron boron (Nd—Fe—B) alloy, is used as the permanent magnet material. This can become prohibitively expense, and the use of a less expensive ferrite material is certainly preferred, although the inferior performance of the ferrite material must be compensated for via a superior magnetic gear assembly design.
As alluded to above, magnetic gear assemblies are ideally suited for use in traction, wind, and ocean power generation applications, among others, where, for example, wave energy converters (WECs) or the like produce very low speed translational motions (e.g. 0.1-2 m/s) or rotational motions (5-20 rpm). Generally, given such low speeds, extremely large or extremely high force density devices are required to generate significant power. Exemplary devices include rotary turbo generators—typically driven by an oscillating airflow, hydraulic motor generators—typically driven by a pressurized fluid, and direct drive linear generators—typically driven by sea motion. It is in conjunction with such devices that magnetic gear assemblies prove to be most valuable at present, although the potential applications are virtually limitless.
Thus, what are still needed in the art are improved low cost magnetic gear assemblies using ferrite magnets or the like, that can provide increased angular velocities and gear ratios, while still providing a contactless mechanism for speed amplification, not requiring lubrication, having inherent overload protection, and having the potential for high conversion efficiency.